The present disclosure relates generally to single-inductor multiple-output (SIMO) based DC-DC converters, more especially to SIMO based converters with adaptive gate biasing (AGB) technique for thermoelectric energy harvesting.
Energy harvested from the environment can be used to develop battery-free electronics systems or prolong battery life. Among the different green energy sources from ambient environment such as light, motion, and heat, thermal power from human body is an efficient and reliable energy source for wearable applications. However, the output voltage of thermoelectric generators (TEGs) is typically less than 100 mV for a thermal difference of 2K depending on the temperature dependent output characteristics range of 10 mV/K to 50 mV/K. Moreover, considering the limited power budget of TEGs, the load system typically requires digital circuits operating in the near-threshold region to reduce power dissipation. Therefore, a power converter that can convert the harvested energy to a near-threshold output is required to realize an energy efficient system. However, designing a high efficiency low-VIN low-VOUT converter is challenging owing to the significant conduction losses (PCONDUCTION) in power transistors.
Numerous thermoelectric energy harvesting power converters have been proposed in the art for low VIN and low power operation. However, the output stages of these power converters are greater than 0.9V. A two-stage topology with a cascaded auxiliary boost converter and a DC-DC buck converter has been proposed, as shown in FIG. 1. An auxiliary boost converter with an additional off-chip inductor LAUX acts as a buffer, and the DC-DC buck converter maintains the VOUT value at 1.8V. With this two-stage topology, the low VIN and low VOUT specifications can be realized because VOUT can be regulated to any desired level. However, this structure in FIG. 1 has low efficiency because of the two-stage conversion and high conversion ratio in the auxiliary boost converter.